Transmission oil composition for automobile

Abstract

A transmission oil composition for an automobile characterized in that it contains a base oil selected from the group consisting of a mineral oil, a synthetic oil and mixtures thereof; and a phosphate compound selected from the group consisting of (A) a zinc dithiophosphate having a hydrocarbon group, (B) a triaryl phosphate (C) a triaryl thiophosphate, and mixtures thereof at 0.1 to 15.0% by mass with respect to the total composition; wherein the composition has a volume resistivity of 1×10 7 ohm·m or more at 80° C.

What is claimed is: 
     
       1. A method of lubricating a transmission system and an electric motor, said method comprising lubricating both the transmission system and the electric motor which share a common lubrication system in an electric vehicle or a hybrid vehicle, with a single lubricant oil composition,
 wherein said composition consists essentially of: 
 a base oil consisting essentially of a synthetic oil selected from the group consisting of 1-octene oligomer, a hydride thereof, 1-decene oligomer, a hydride thereof, ethylenepropylene oligomer, a hydride thereof, di-tridecyl glutarate, di-2-ethylhexyl adipate, di-isodecyl adipate, di-tridecyl adipate, di-2-ethylhexyl sebacate, trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, neopentyl glycol 2-ethylhexanoate, and mixtures thereof, 
 a phosphate compound selected from the group consisting of (B) a triaryl phosphate at 0.2 to 1.0% by mass with respect to the total composition, (C) a triaryl thiophosphate at 0.4 to 1.5% by mass with respect to the total composition, and mixtures thereof, and 
 (D) an ashless dispersant selected from the group consisting of a nitrogen-containing compound having in its molecule at least one alkyl or alkenyl group having 12 to 400 carbon atoms, and a derivative thereof, at 10 to 400 ppm by mass in terms of nitrogen atom with respect to the total composition, wherein said ashless dispersant has a succinimide portion, 
 wherein said composition has volume resistivity of 5×10 8  ohm·m or more at 80° C., 
 wherein the kinematic viscosity of said composition at 80° C. is 1.5 to 3.5 mm 2 /s. 
 
     
     
       2. The method according to  claim 1 , wherein said transmission system and said electric motor are included in a packaged device. 
     
     
       3. The method according to  claim 1  wherein said composition requisitely comprises a triaryl phosphate at 0.2 to 1.0% by mass with respect to the total composition. 
     
     
       4. The method according to  claim 1  wherein said composition requisitely comprises a triaryl thiophosphate at 0.4 to 1.5% by mass with respect to the total composition. 
     
     
       5. The method according to  claim 1 , wherein a water content in said composition is not more than 1000 ppm by mass. 
     
     
       6. The method according to  claim 1 , wherein a content of said ashless dispersant in said composition is not less than 10 ppm and not more than 2000 ppm by mass in terms of nitrogen atom. 
     
     
       7. The method according to  claim 1 , wherein said composition further comprises other additives selected from the group consisting of amine antioxidant, benzotriazol, polymethacrylate, and dimethylsilicon. 
     
     
       8. The method according to  claim 1 , wherein said composition further comprises additives selected from the group consisting of a metal detergent, an extreme pressure agent and an anti-wear agent other than said components (B) and (C), an antioxidant, a viscosity index improver, a rust inhibitor, an anti-static agent, a corrosion inhibitor, a pour point depressant, a rubber or seal sweller, an antifoam agent, and a coloring agent. 
     
     
       9. The method according to  claim 1 , wherein a content of said ashless dispersant in said composition is not less than 60 ppm and not more than 400 ppm by mass in terms of nitrogen atom.